Process for preparing homogeneously partially polymerized particles of thermosetting material



July 25, 1950 G. w. BORTON ETAL 2,515,295

' PROCESS FOR PREPARING HOMOGENEOUSLY PARTIALLY POLYMERIZED PARTICLES OF THERMOSETTING MATERIAL Filed Aug. 9, 1946 3 Sheets-Sheet l FIG. 4.

FIG. 5.

lNVE/VTOQJ. STANLEY D HAPTSHORN GEORGE W 80? TON July 25, 1950 Filed Aug. 9, 1946 G. W. BORTON ETAL PROCESS FOR PREPARING HOMOGENEOUSLY PARTIALLY POLYMERIZED PARTICLES 0F THERMOSETTING MATERIAL 3 Sheets-Sheet 2 lA/VENTORS. STANLEY Q HARTSHOPN GEORGE W 802 TON WWW July 25, 1950 G. w. BORTON ETAL 2,515,295

PROCESS FOR PREPARING HOMOGENEOUSLY PARTIALLY POLYMERIZED PARTICLES 0F THERMOSETTING MATERIAL Filed Aug. 9, 1946 3 Sheets-Sheet 3 R ATION DR AND ROTOR 7 l6 II/II/II;

A T TOR VE K Patented July 25, 1950 UNITED TATES PATENT orsrcs 2,516,295 PROCESSFO -E NGT OMO'GENEQUS- LY. PARTIALLY POLYMERIZ'ED PARTICLE-S F THERMOSETTING MATERIAL George W. Burton, Philadelphia, :and Stanleyl). Hartshorn, Wayne, Pa a ssignors to Pennsylvania GrushenCompany, .Bhiladelphia, 'Pa.,'a corporation of New York Application August 9, 1946;4Seria1iNoA68937 2 =2 Claims. 1

This invention relates to the manufactureof plastics and more particularlyto a-system for th'e production of uniform moldable'plastic particles.

It is an object-of this invention to provide a process for preservatio'nof 'homogeneouspolymerization of a plasticby uniform reductionto small particles.

It is a further object-of thisinvention to pro- =vide a process for reduction of -'a "plastic material tohomogeneously polymerized particles.

Other and further objects will appear" from the following description taken together with the figures in which:

Fig. 1 is "a side View of apparatus for preparing and reducing a polymerizable substance;

' Fig. 2 i is a vertical longitudinal sectional i'view of a bradmill;

FigQBfis a verticalsection taken onlinef3 3 of Fig. 2;

'Fig. 4 is a perspective view of a particlera fter breaking the po'lymerizablesubstance in the'sawtooth crusherof Fig. 1 and bfore-reductionlin the bradmill. of Fig. 2; and

Fig. 5is a perspective View of=-a typical-particle after reduction.

In general,-this inventionrelates to the..preparation of a polyin'erizable :material; in which :8 partially polymerizedmaterial :israpidly reduced '--to particles to maintain: a homogeneity? of polymerization.

Referring to Fig. 1, a vat I is shown- -in:which=,1s placed a pl-astic such as a; phenol-formaldehyde :condensation; product. Whempassed into the-vat I this I plastic has been :.Drocess'ed to =;the :point Where it is -softavhenheatedrandiharcliwhen cooled and. is homogeneously in'i astage ofapartial polymerization. .The .plastic masslis maintained in a heated. and plastic, homogeneous condition vat I into the heatedrolls fii 'where it is co'mpressed 'into a strip 3 approximately inithickness. "By attenuating the: plastic mass intoa thiri stri'p it can be cooled rapidly. This rapi'd: cdoling is important in"bringing about a uniioi m decrease in the rate of-polymeriz'at'ion W ich is i'educed upon the cooling of the plastic. Wis the-strip is cooled almost instantaneously upon leaving the rolls 2, and the rate of polyiiierization correspondingly affected, the polymerization I of all portions stiff strip of homogeneously, partially pciymeri ized plastic is obtained. The brittle -strip --is 'subsequently f fed into a 1 saw-tooth crusher 4 which-chops the *piec'es 3 up'into pieces scrap- (Cl. I S- 47:5)

proximately 1/ 1 to 1 1% --;in -:width .or-ilengthand in thickness. Atypical chip 5 formed ihy breaking the strip 3 in the .crusher k is shown; in Fig.4. 5 The chipsr 5-fallirom the saw-tooth crusherg d onto a continuous belt6= which carriesrthemato the pradrhill crusher The bradrnill crusher I *showniin Fig. Ziscomprisefdof a drumwrotating son-2a horizontal:axisnin a casing-9.

-1 ig.:3-ais' a radial section .of the :bradmilhshowing the .cdrum 8 rotating counterclockwise.:zatid having a screen I I around its.i perirrreter perforated with perforations I0 to .permit 'vpassagerroi p'articles I5 of the order of "10 mesh :sieve size. The shelves I2, I23 and-Marepositioned infizhe drum 8 having imp'act surfaces forming angles of? 2.0 degrees to 35 degrees with the .radius of the drum 8.

A hammer carrying I rotor assembly t8 rotates "counterclockwisecoax-ially with 'dr-uin B and 1' car- -r-ies hammers IQ for striking the polymerize-hie material with-surfaces 2|. -The 'chips 5 when str-uck by the fafst m'oving surfaces 2| are frac- 'turedflcy the impact and thrust against thesnrfacesiB-of the shelves I2, I3-and I4. The-result- "in'g -particles I5 suffer further "fracturing by he "secon'climpact and'either-ialrto the, screen II-or :continueto be struck bjy 'impact sur'faceS II'S-and 21 until-theyfall tothescreenII. The -shelves "carrying surfaces I! of the; shelves l l'exten'd to and" are contiguous with 'the'screenll Whi1e"'the "carrying surfaces ll"'of"the"she'1ves "i3 extend. toward but'iare spacednway *from the screen "I-I "-The shelves IZ having no carryingsurfacesfare spaced f-urther awayfrom thescreen I I thanthe "carryingsurfaces "I1. Theparticles IB on the 40 1 screen II are "therefore free to" slide" underthe shelves I2 and I3 and catching on the? surfaces "I"! are carried'upward-withthe rotation o ffthe drum B. *In the sliding action 'of the'fractured "particles onthe "moving screen "I I -the parti 'cles are tumbled over "each other. andithose lessfthan a predetermined size set by the perforations m pass through "the perforations t0 and'j' into "the "casing 9' from "which "they fall thrdughjaf'discharge opening 22. The particles greater than "'thefpredetermined size and too large" for; passage through the perforations "It arecarried upward on thesurfaces II bythe rotation of'the drum andiat theftop of the cycle dropo'fifinto' the gpath Tof thefhammer 'surfaces ZI and are subjected'lto "fuitlier-"fracturing 'b'y impact. "Thisproc'ess is on a shaft 25 by collars 21 to form a rotor assembly l8. On the end of shaft 26 is provided an L-shaped member which forms a rigid hammer 28 having impact surfaces 29. This hammer 28 and its surfaces 23 cooperate with the hammers l9 and the surfaces 2| to fracture the particles 5.

The chips are fed into the drum 8 through a chute 3| formed in one side of the casing 9. The drum 8 and the shaft 26 are driven through an opening in the side of casing 9 opposite chute 31. A pair of pulley blocks 32 support a rotatable quill 33'which carries the drum 8 on a flanged end 34 extending into the casing 9. The quill 33 is turned by sprocket 36 driven by suitable means. The shaft is carried inside the quill 33 on bearings 31 and the shaft is driven by a pulley 38 powered by suitable means.

The process operates as follows: A polymerizable substance such as phenol-formaldehyde condensation compound which has been prepared and has polymerized into a plastic mass when heated is placed in the vat I. This mass continues to polymerize in the vat l and would eventually assume a hard and infusible nature. While the mass in the vat l is in the plastic when hot but stiff when cool state, it is fed out of the vat I through heated rolls 2 which compress the mass into a thin wide strip of approximately 4" thickness. This thin strip 3 is rapidly and evenly cooled because of its thinness and the rate of polymerization which is substantially loweredby the decrease in temperature is uniformly reduced for all parts of the strip as it leaves the rolls 2. The homogeneity of the partial polymerization thus attained in the material strip 3 is preserved by rapidly reducing the plastic to particles ii of uniform size in which size the further polymerization of the plastic is uniform. To obtain this reduction the hardened strip is immediately cracked up in the saw-tooth crusher 4 and the particles 5 of plastic material from the crusher 4 drop onto a continuous belt 6 and are carried down to chute 3| of the bradmill 1. The particles 5 dropping into the chute 31 slide into the rotating drum 8 and are picked up on the shelves l2, l3 and [4 by the rotation and carried upward to the top of the cycle from which they are 'dropped into the path of the rapidly rotating rotor l8 and struck by the hammer surfaces 2| to be fractured by impact. After bouncing off the impact surfaces 2! and I6, as before mentioned, the fractured particles l5 collect on the screen I l and sliding over the screen upon rotation of the drumli the smaller particles fall through the perforation and out into casing 9 thence through discharge opening 22. As before mentioned, those over-size particles too large to pass through the perforations H] are carried upward by the rotation of drum 8 for a repetition of the fracturing procedure.

It is desired to remove the particles l 5 from the bradmill I as soon as they have been reduced to the proper size for passage through screen H. It is also necessary to reprocess those oversize particles which have not been suificiently re- ,duced. To separate the'two sizesthemixture oflzzflfi cooling said material substantially instantaneparticles I 5 that falls on the screen I I slides over the screen I I as the drum 8 rotates. This sliding tumbles and tosses the loose particles 15 on the rotating surface of screen H so that the IO-mesh sieve particles-are given an opportunity to drop through the perforations Hi before being carried upward and unnecessarily reprocessed. The carrying surface ll of the shelf 13 assists in obtaining a good mixing of the various sized particles by leveling off the particles that have fallen onto the screen H and preventing a pile-up which would trap the under-size particles away from the screen.

By this process a particle of the strip 3 is broken, fractured, sorted and passed out for further processing in a short time. A particle is reduced to a desired size quickly to prevent any more polymerization of large particles than is necessary. This is important as uneven polymerization decreases with the size of .the individual particle of polymerizable plastic. In small polymerizable particles the condensation process is essentially equal in all parts of the particle and equivalent sizes of polymerizable particles under equivalent conditions have equivalent rates of polymerization. Therefore, the preservation and creation of homogeneity in the polymerization of a condensation product or other polymerizable plastic is aided by reducing the plastic to particles in which the rate of polymerization will be substantially the same for all parts of the material in all the particles.

This process achieves the preservation of homogeneity of the polymerization by minimizing the period during which the polymerizable material is formed in large pieces and by reducing it to small particles as rapidly as possible. This process also has the advantage of subjecting the polymerizable material to fracturing only to the extent that is necessary for attaining the desired small particle by removing the small particle from the fracturing device as soon as it has achieved the desired smallness. The final product has a very small percentage of dust due to the perpetual alternate screening and crushing so that the finer particles are screened out as soon as they are produced. The

rate of pour, for instance, through a funnel orifice, is excellent as is the weight per cubic centimeter, the size of the particles being graduated and averaged to very compactly fill in the intervening spaces.

Various modifications of the apparatus disclosed may be employed in carrying out the method of this invention. For instance, the sawtooth crusher 4 may be of the single roll type and the times of treatment will be regulated according to the characteristics of the material. After the preliminary polymerization the material isv cooled and kept below a temperature at which there is any substantial polymerization so that the final crushing may be timed at any convenientcinterval. The invention is not intended to be restricted to the specific embodiments shown but isintended to cover such modifications thereof as fall within the appended claims.

What is claimed is:

1.- A.processfor preparing homogeneously partially polymerized particles of plastic material suitable for, storing prior to molding and complete polymerization comprising preparing the material for a composition setting under the action of heat, giving the material a preliminary heat treatment to partial polymerization and ously to hardened condition of predetermined desired thinness and brittleness preparing the material to be fractured by a hammer blow against freely suspended pieces, immediately reducing said thin material to pieces of desired small size, maintaining said material below a temperature at which there is any substantial polymerization, then introducing said thin pieces as freely-moving units into the path of a fast-moving surface and subjecting said pieces while freely moving to fracture by said fast-moving surface, projecting the resulting fractured particles from said surface freely through the air against another surface causing further fracture of said particles to smaller size as said particles break themselves against said second surface so that said fracturing is due to the inertia of the pieces and particles when engaged by said surfaces, outwardly discharging fractured particles of predetermined small size from around the periphery of said 6 the same time maintaining uniformity in the partial polymerization of the final particles.

2. A process for preparing homogeneously partially polymerized particles of plastic material as set forth in claim 1 in which the thin pieces of material are approximately 4" thick and about to 1 in longest surface dimension.

GEORGE W. BOR'ION. STANLEY D. HARTSHORN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,586,850 Smith June 1, 1926 1,977,771 McMahon Oct. 23, 1934 1,996,757 Elbel Apr. 9, 1935 2,015,711 Cherry Oct. 1, 1935 2,155,150 Schacht Apr. 18, 1939 2,161,748 Samaras et al. June 6, 1939 2,211,518 Scherbaum Aug. 13, 1940 2,229,291 Groten et a1. Jan. 21, 1941 2,335,515 Jehle Nov. 30, 1943 2,346,708 Smidth Apr. 18, 1944 

1. A PROCESS FOR PREPARING HOMOGENEOUSLY PARTIALLY POLYMERIZED PARTICLES OF PLASTIC MATERIAL SUITABLE FOR STORING PRIOR TO MOLDING AND COMPLETE POLYMERIZATION COMPRISING PREPARING THE MATERIAL FOR A COMPOSITION SETTING UNDER THE ACTION OF HEAT, GIVING THE MATERIAL A PRELIMINARY HEAT TREATMENT TO PARTIAL POLYMERIZATION AND COOLING SAID MATERIAL SUBSTANTIALLY INSTANTANEOUSLY TO HARDENED CONDITION OF PREDETERMINED DESIRED THINNESS AND BRITTLENESS PREPARING THE MATERIAL TO BE FRACTURED BY A HAMMER BLOW AGAINST FREELY SUSPENDED PIECES, IMMEDIATELY REDUCING SAID THIN MATERIAL TO PIECES OF DESIRED SMALL SIZE, MAINTAINING SAID MATERIAL BELOW A TEMPERATURE AT WHICH THERE IS ANY SUBSTANTIAL POLYMERIZATION, THEN INTRODUCING SAID THIN PIECES AS FREELY-MOVING UNITS INTO THE PATH OF A FAST-MOVING SURFACE AND SUBJECTING SAID PIECES WHILE FREELY MOVING TO FRACTURE BY SAID FAST-MOVING SURFACE, PROJECTING THE RESULTING FRACTURED PARTICLES FROM SAID SURFACE FREELY THROUGH THE AIR AGAINST ANOTHER SURFACE CAUSING FURTHER FRACTURE OF SAID PARTICLES TO SMALLER SIZE AS SAID PARTICLES BREAK THEMSELVES AGAINST SAID SECOND SURFACE SO THAT SAID FRACTURING IS DUE TO THE INERTIA OF THE PIECES AND PARTI- 